STOCKHOLM — The list of troubles linked to Justin Bieber's tour of Europe grew again after Swedish police said Thursday they had found drugs and a stun gun on the pop singer's bus.

No arrests were made since the bus was empty at the time, Stockholm police spokesman Lars Bystrom told The Associated Press.

Police said they decided to act after smelling marijuana coming from inside the bus while it was parked outside the hotel where Bieber was staying in the capital. Drug officers searched the bus during the concert while Bieber was on stage, Bystrom said.

He said a small amount of drugs and a stun gun were discovered during a search of the bus, which had been parked under the Globen concert venue in Stockholm, where Bieber was performing Wednesday. Bystrom declined to identify the drug, saying that it was sent to a lab for analysis.

Bieber, who arrived in Helsinki, Finland, later Thursday to perform in a concert the following evening, tweeted after his arrival: "some of the rumors about me....where do people even get this stuff. whatever...back to the music."

The incident is the latest in Bieber's tumultuous European tour, which has included a monkey detention, a Holocaust museum furor and a health scare.

In Britain, the 19-year-old singer struggled with his breathing and fainted backstage at a London show. He was taken to a hospital, only to be caught on camera clashing with paparazzi.

The Canadian teenage idol had to leave his monkey in quarantine in Germany since he didn't have the necessary papers for the animal.

Bieber then became the focus of intense criticism in the Netherlands for writing an entry into a guestbook at the Anne Frank House museum in Amsterdam, saying he hoped the Jewish teenager, who died in a Nazi concentration camp, "would have been a Belieber" — or fan of his — if her fate had turned out differently.

The comment provoked a flood of comments on the museum's Facebook page, with many people criticizing the singer for gross insensitivity.

Anne Frank hid with her family in a small apartment above a warehouse during the Nazi occupation of World War II. Her family was caught and deported, and Anne died of typhus in Bergen-Belsen in 1945. She was 13 years old when she began keeping her diary in 1942. Like many teenage girls, she made a collage of the celebrities of her day — movie stars, dancers, and royalty — and kept it on her bedroom wall.

In Norway, where Bieber enjoys enormous popularity, education officials in a remote district rescheduled midterm exams for high school students so that the singer's fans could attend the concert in the capital and not have to worry about missing the tests.